P-Selectin expression, platelet aggregates, and platelet-derived microparticle formation are increased in peripheral arterial disease.

Platelet volume has been reported to be increased in vascular disease. Therefore, we studied the relationship of mean platelet volume and platelet count as well as flow cytometrically measured platelet size and platelet function in 50 patients with peripheral arterial disease and 50 healthy volunteers. Platelet activation was measured by P-selectin expression analysis on resting and on stimulated platelets, and the determination of platelet aggregates and platelet-derived microparticles using flow cytometry. P-Selectin expression on platelets was significantly elevated in patients suffering from peripheral arterial disease (all P<0.0001). Platelet aggregates (P<0.0001) and platelet-derived microparticles (P<0.0001) were significantly higher in the patient group compared with controls, whereas mean platelet volume and platelet count showed no significant differences. Platelet count was inversely related to mean platelet volume in patients and controls (r = -0.43, P<0.001). The present study supports the hypothesis of platelet hyperreactivity and circulating activated platelets in peripheral arterial disease. Mean platelet volume, and platelet count cannot be used as predictive markers for platelet activation in peripheral arterial disease patients.     

Pathobiology of pulmonary hypertension. The role of platelets and thrombosis

With the rare exceptions of PAH associated with antiphospholipid antibodies, genetic platelet dysfunction, or inherited deficiencies of antithrombotic pathways, the thrombotic lesions are secondary, but frequently occurring, in most cases of primary or secondary PAH. Pulmonary arterial hypertension is associated with thrombotic lesions and persistent vasoconstriction and structural remodeling of PA. Activated platelets interact with the PA wall and may contribute to the functional and structural alterations of pulmonary vessels by releasing vasoactive factors and mitogenic mediators.     

Platelet-induced differentiation of endothelial progenitor cells

Endothelial progenitor cells (EPCs) have the potential to home at sites of vascular lesions and to contribute to revascularization. This homing is a highly concerted mechanism, which involves chemotaxis, adhesion, migration, and finally integration of the cells into the target tissue. Only recently has the platelet been identified as a central mediator of EPC homing. Adherent platelets were able to mediate chemotaxis and adhesion of EPCs, a process that involved P-selectin glycoprotein ligand 1 and very late antigen-4 (VLA-4). Recent studies suggest that platelet-derived stromal cell-derived factor-1 is also involved centrally in the recruitment of EPCs. Furthermore, platelets induce progenitor cell migration by platelet-derived growth factor AB. Recent in vivo data confirm the recruitment of EPCs to sites of vascular lesions after vessel denudation by activated platelets and fibrin. Moreover, when coincubated with platelets, EPCs differentiate to mature endothelial cells and have the potential to migrate and colonize a platelet thrombus. The described interaction of EPCs with platelets represents a novel mechanism of vascular remodeling and healing of endothelial lesions.     

Platelets and platelet-derived serotonin promote tissue repair after normothermic hepatic ischemia in mice

Hepatic ischemia and reperfusion (I/R) leads to the formation of leukocyte-platelet aggregates. Upon activation, platelets generate reactive oxygen species and release proapoptotic and proinflammatory mediators as well as growth factors. In cold hepatic ischemia, adhesion of platelets to endothelial cells mediates sinusoidal endothelial cell apoptosis. Furthermore, platelet-derived serotonin mediates liver regeneration. We hypothesized that platelets may contribute to reperfusion injury and repair after normothermic hepatic ischemia. The aim of this study was to assess the impact of platelets in normothermic hepatic I/R injury using models of impaired platelet function and immune thrombocytopenia. Inhibition of platelet function in mice was achieved via clopidogrel feeding. Immune thrombocytopenia was induced via intraperitoneal injection of anti-CD41 antibody. Platelet-derived serotonin was investigated using mice lacking tryptophan hydroxylase 1. Mice were subjected to 60 minutes of partial hepatic ischemia and various time points of reperfusion. Hepatic injury was determined via AST and histological analysis of the necrotic area as well as leukocyte infiltration. Liver regeneration was determined via proliferating cell nuclear antigen and Ki67 immunohistochemistry. Neither inhibition of platelet function nor platelet depletion led to a reduction of I/R injury. Liver regeneration and repair were significantly impaired in platelet-depleted animals. Mice lacking peripheral serotonin were deficient in hepatocyte proliferation, but otherwise displayed normal tissue remodeling. Conclusion: Platelets have no direct impact on the pathogenesis of normothermic I/R injury. However, they mediate tissue repair and liver regeneration. Furthermore, platelet-derived serotonin is a mediator of hepatocyte proliferation in the postischemic liver, but has no impact on tissue remodeling.     

The significance of platelet-derived growth factors for proliferation of vascular smooth muscle cells

Platelets are important in acute thrombotic occlusion of injured vessels, e.g., subsequent to angioplasty. In contrast to these acute events of thrombus formation, much less is known about the significance of platelets for the control of smooth muscle cell (SMC) proliferation. A body of experimental and clinical evidence indicates an involvement of platelets in the pathology of atherosclerosis and restenosis. However, the precise role of platelet-derived growth factors for SMC proliferation in atherosclerotic and restenotic vessels is not clear and many questions remain unresolved. Platelet-dependent SMC mitogenesis is determined by a coordinate action of several classes of mitogenic factors which are either released from storage pools or generated upon platelet activation. Although platelet-derived growth factor (PDGF) is considered to be the most important platelet mitogen it is very likely that yet unknown factors and mechanisms are involved. Differential (stimulatory or inhibitory) effects on SMC growth and differentiation have been reported for different platelet-derived growth factors. Thus, for the overall response, complex interactions between multiple factors need to be considered. In addition, multicellular interactions, e.g., between platelets and endothelial cells may modulate the effects of platelet-derived factors on SMC mitogenesis. Taken together, the mechanisms of platelet-dependent SMC proliferation need to be reevaluated. The assessment of the precise role of platelet mitogens in the complex proliferative repair mechanisms of an injured vessel wall clearly requires further studies.     

The significance of platelet-derived growth factors for proliferation of vascular smooth muscle cells

Platelets are important in acute thrombotic occlusion of injured vessels, e.g., subsequent to angioplasty. In contrast to these acute events of thrombus formation, much less is known about the significance of platelets for the control of smooth muscle cell (SMC) proliferation. A body of experimental and clinical evidence indicates an involvement of platelets in the pathology of atherosclerosis and restenosis. However, the precise role of platelet-derived growth factors for SMC proliferation in atherosclerotic and restenotic vessels is not clear and many questions remain unresolved. Platelet-dependent SMC mitogenesis is determined by a coordinate action of several classes of mitogenic factors which are either released from storage pools or generated upon platelet activation. Although platelet-derived growth factor (PDGF) is considered to be the most important platelet mitogen it is very likely that yet unknown factors and mechanisms are involved. Differential (stimulatory or inhibitory) effects on SMC growth and differentiation have been reported for different platelet-derived growth factors. Thus, for the overall response, complex interactions between multiple factors need to be considered. In addition, multicellular interactions, e.g., between platelets and endothelial cells may modulate the effects of platelet-derived factors on SMC mitogenesis. Taken together, the mechanisms of platelet-dependent SMC proliferation need to be reevaluated. The assessment of the precise role of platelet mitogens in the complex proliferative repair mechanisms of an injured vessel wall clearly requires further studies.     

Low-density platelet populations demonstrate low in vivo activity in sporadic Alzheimer disease

Platelets contain a substantial quantity of amyloid-precursor protein (APP) and β-amyloid. However, despite the large importance of APP and β-amyloid to dementia, little is known about platelets in sporadic Alzheimer dementia (AD). Furthermore, platelet heterogeneity influences human pathology and has been described to affect the progression of AD. This study investigated AD platelets with respect to density diversity and in?vivo activity associated with density sub-fractions. We included 39 AD patients and used, as controls, 22 elderly individuals without apparent memory disorder. A continuous Percoll? gradient covering the density span 1.04-1.09?kg/l provided the basis to divide platelets of whole blood into density fractions (n?=?16). All platelet populations were evaluated accordingly. Platelet counts were determined electronically. A flow-cytometer was put to use to measure surface-bound fibrinogen as a measure of platelet in?vivo activity. Samples obtained from patients diagnosed with sporadic AD contained platelets (fractions numbers 4-16) that circulated with significantly less surface-bound fibrinogen, i.e., their platelet activation in?vivo was reduced, compared with controls. In particular, highly significant differences (p?相似文献   

Golgi complexes in hypogranular platelet syndromes

The white platelet syndrome (WPS) is an autosomal dominantly inherited hypogranular platelet disorder characterized by the presence of fully developed Golgi complexes from parent megakaryocytes in 13% or more of their circulating platelets. The present study has evaluated several other hypogranular platelet disorders to determine if perpetuation of Golgi complexes in circulating cells is a common link in those inherited conditions. Only platelets from patients with the gray platelet syndrome (GPS) and one patient with α?δ platelet storage pool deficiency (α?δ SPD) had more Golgi complexes in their cells than were found in normal thrombocytes. Platelets from patients with the Hermansky–Pudlak syndrome, two other patients with α?δ SPD and the individual with Medich giant platelet disorder had the same frequency of Golgi complexes in circulating cells as normal controls. Thus, the presence of large numbers of fully developed Golgi complexes in circulating platelets appears unique to the WPS.     

The effect of hormone replacement therapy on Ca2+ mobilization and P-selectin (CD62P) expression in platelets examined under flow cytometry.

A series of events, such as increase of cytoplasmic free calcium (Ca2+) and expression of P-selectin (CD62P), an adhesion molecule, on the platelet surface, are significant indicators of platelet activation. We have used flow cytometry to examine Ca2+ mobilization and CD62P expression in platelets in whole blood obtained in women prior to, and after, different forms of hormone replacement therapy. Thirty-two women completed a protocol consisting of two consecutive 1-month periods under oestradiol (E2), administered orally (2 mg/day) or transdermally (50 microg/day) in random order, followed by a 4-week transdermal sequential regime, in which, during the last 14 days, either progesterone (300 mg/day) or medroxyprogesterone acetate (5 mg/day) was added to the 50 microg/day E2, administered orally in random order. None of the hormonal combinations determined significant changes in Ca2+ mobilization or CD62P expression in non-stimulated platelets. However, stimulation of platelets with adenosine diphosphate, but not with thrombin, caused a significant increase in cytoplasmic Ca2+ concentration during treatment with transdermal E2 plus progesterone. Also when stimulating with thrombin, transdermal E2 was more active than oral E2 in increasing CD62P expression, a difference that was not reduced by the addition of progestogens. In conclusion, hormone replacement therapy only increased Ca2+ mobilization or CD62P expression in stimulated platelets, and then followed a varied pattern that was dependent on the stimulant and on the specific hormonal formulation.     

Platelet-derived growth factors

Blood platelets are a rich source of growth factors, including platelet-derived growth factor, platelet-derived endothelial cell growth factor, and transforming growth factor beta. Platelet-derived growth factor stimulates the growth of mesenchymal cells such as fibroblasts and vascular smooth muscle cells, whereas platelet-derived endothelial cell growth factor is a mitogen for vascular endothelial cells. Transforming growth factor beta is a bifunctional regulator of cellular growth, but acts as a potent inhibitor for most cell types. Most of the growth regulatory substances in platelets have been reported to reside in platelet alpha-granules, but platelet-derived endothelial cell growth factor appears to be present in platelet cytoplasm. These growth factors may act at sites of injury as wound hormones. Moreover, they play important roles for some pathological conditions such as atherosclerosis, myelofibrosis, connective tissue diseases, and neoplastic disorders.     

Pathological events in platelets of Wiskott-Aldrich syndrome patients

The Wiskott-Aldrich syndrome (WAS) is a severe X-linked platelet/immunological disorder arising from mutations of the gene WASP. At the clinical level, the major platelet abnormalities are small size and low number, both partially correctable by splenectomy. To identify underlying pathological events, we examined WAS platelets at various stages of their lifetime. In spleen sections from WAS patients, fluorescence microscopy showed dramatic co-localization of markers of platelets (CD41) and macrophages (CD68) compared to non-thrombocytopenic controls, suggesting that WAS splenic macrophages are involved in platelet removal. Study of isolated WAS blood platelets by flow cytometry showed substantial enhancement of surface exposure of phosphatidylserine (PS), a signal for engulfment by macrophages. Isolated resting WAS platelets were also aberrantly susceptible to microparticle release, and plasma samples of WAS patients contained > 5 times normal numbers of platelet-derived microparticles which may explain the small size of circulating platelets. Measurements with the Ca2+ sensitive dye fluo-3 revealed significantly increased Ca2+ levels, 310 +/- 13 nmol/l for WAS platelets versus 106 +/- 12 nmol/l for normal platelets, and also prolongation of agonist-induced Ca2+ flux. Cumulatively, these studies identify abnormal events occurring in WAS platelets: increased Ca2+ levels and enhancement of two Ca2+ dependent processes, PS exposure and microparticle release; these abnormal events may contribute to the in vivo decrease of platelet number and reduction of platelet size in this disease.     

Effect of transdermal hormone replacement therapy on the monocyte chemoattractant protein-1 concentrations and other vascular inflammatory markers and on endothelial function in postmenopausal women

Monocyte chemoattractant protein-1 (MCP-1) is related to the progression of atherosclerosis. However, little is known about the effects of transdermal hormone replacement therapy (HRT) on circulating MCP-1, vascular inflammatory marker concentrations, and endothelial function in postmenopausal women. The effects of transdermal HRT on circulating MCP-1, vascular inflammatory marker concentrations, and endothelium-dependent vasodilation were investigated in postmenopausal women. Thirty-three women received transdermal HRT (continuous 17-beta estradiol patch 36 microg/day plus cyclic oral medroxyprogesterone acetate 2.5 mg/day for 12 days/month) for 12 months, and 27 control patients did not. Brachial artery flow-mediated vasodilation (FMD), assessed by ultrasound, and circulating MCP-1 and vascular inflammatory marker (C-reactive protein, intercellular adhesion molecule-1 [ICAM-1], vascular cell adhesion molecule-1 [VCAM-1], and E-selectin) concentrations were measured before and after 12 months of treatment. In the HRT group, MCP-1 concentrations decreased significantly (p <0.001), and ICAM-1, VCAM-1, and E-selectin concentrations decreased significantly (p <0.01 for all), but C-reactive protein concentrations did not change. MCP-1 and other marker concentrations did not change in the control group. FMD increased significantly in the HRT group (p <0.001) but did not change in the control group. Nitroglycerin-induced vasodilation did not change in either group. In conclusion, transdermal HRT decreased MCP-1 and cell adhesion molecule concentrations and improved endothelial function in postmenopausal women. Transdermal HRT may exert an antiatherosclerotic effect by improving MCP-1 and cell adhesion molecule expression and endothelial function.     

Abnormal levels of platelet-specific proteins and mitogenic activity in myeloproliferative disease.

It has been postulated that platelet-derived growth factor and platelet factor 4 (PF4) are involved in the imbalance of the mechanism of medullar stroma maintenance which triggers off the bone marrow myelofibrotic process. In this work we compare the PF4 and the beta-thromboglobulin (beta-TG) and mitogenic activity in platelet-poor plasma (PPP) and platelet extracts (PE) from patients with myeloproliferative disorders (MPD) with those of secondary thrombocytosis (ST) and normal volunteers. Statistically significant differences were found between MPD and ST patients or controls, but none between ST and controls in all the parameters studied. Maximal differences in platelet-derived factors (PDFs) between MPD and control groups were found in polycythemia vera patients. However, the relationship between the presence of myelofibrosis and abnormal levels of beta-TG, PF4 and mitogenic activity in PPP and PE was only observed in patients with agnogenic myeloid metaplasia (AMM). These results show that PDFs are specifically decreased in MPD platelets. Furthermore, no statistical correlation was found between PDFs and the number of platelets. However, other unknown factors or conditions would be necessary to develop myelofibrosis in MPD, which is present in AMM.     

Effects of erythropoietin on platelet reactivity and thrombopoiesis in humans

A recent study in dogs suggested that erythropoietin (EPO) not only promotes the synthesis of increased numbers of reticulated platelets but that these newly produced platelets are hyperreactive compared with controls. Because of the increasing use of EPO in the perioperative setting, we characterized the effects of EPO on platelet reactivity in healthy human volunteers. In a randomized, controlled trial, we studied the effects of EPO on platelet reactivity, thrombopoiesis, and endothelial activation in circumstances similar to those of autologous blood donation. Thirty healthy male volunteers received placebo or EPO (100 or 500 U/kg of body weight given intravenously) three times a week for 2 weeks and underwent phlebotomy on days 8 and 15. Thrombin receptor-activating peptide induced expression of P-selectin, and CD63 increased 2- to 3-fold during EPO treatment. The enhanced platelet reactivity was also reflected by a 50% increase in soluble P-selectin in plasma. Plasma E-selectin levels increased in a dose-dependent fashion by more than 100% during EPO treatment, indicating substantial activation of endothelial cells. A 10% to 20% increase in platelet counts was observed in both EPO groups on day 5. In the placebo group, platelets increased only several days after the first phlebotomy. The increase in platelet counts was not reflected by changes in the amounts of reticulated platelets or circulating progenitor cells. In summary, we found that EPO markedly enhances endothelial activation and platelet reactivity, which may adversely affect patients at cardiovascular risk. However, the increased platelet reactivity could be exploited in patients with platelet dysfunction. (Blood. 2000;95:2983-2989)     

Role of platelets and thrombosis in mechanisms of acute occlusion and restenosis after angioplasty

The vascular disruption produced by angioplasty initiates platelet deposition through the processes of platelet adhesion and recruitment of circulating platelets to form an enlarging mural platelet thrombus. Thrombin produced by simultaneous activation of the coagulation cascade by subendothelial connective tissue structures enhances platelet deposition and stabilizes the forming thrombus with enmeshing fibrin. Platelet recruitment involves the expression of the glycoprotein IIb/IIIa receptor for fibrinogen and other cytoadhesive proteins including fibronectin, thrombospondin and von Willebrand factor. Platelet deposition and thrombus formation caused by angioplasty appear to be important in the development of 2 complications: acute thrombotic occlusion and restenosis. Experimental mechanical vascular injury produces a predictable, although rather variable, amount of vascular narrowing due to transient smooth muscle cell proliferative intimal lesion formation. This intimal thickening by proliferating smooth muscle cells is in part mediated by platelet mitogens, particularly platelet-derived growth factor, which are released into the damaged vessel from platelets at the time of angioplasty. Platelet-derived growth factor may also be released from other associated vascular and blood cells in response to mechanical injury, e.g., endothelium, monocyte/macrophage and smooth muscle cells themselves. The actual mitogens, and their cells of origin, that mediate restenosis after therapeutic angioplasty remain to be established. Various oral antiplatelet agents have been shown to reduce arterial thrombotic occlusion in a number of controlled clinical trials, e.g., aspirin in transient ischemic attacks and unstable angina, aspirin and dipyridamole in saphenous vein coronary artery bypass and progression of peripheral vascular disease and dipyridamole in artificial heart valves. Acute arterial thrombosis may require more potent, immediate and transient intervention, e.g., monoclonal antibody to platelet receptor expression.(ABSTRACT TRUNCATED AT 250 WORDS)     

Laboratory markers of platelet activation and their clinical significance.

Whole blood flow cytometry is a powerful new laboratory technique for assessment of platelet activation and function. Flow cytometry can be used to measure platelet hyperreactivity, circulating activated platelets, leukocyte-platelet aggregates, and procoagulant platelet-derived microparticles in a number of clinical settings, including acute coronary syndromes, angioplasty, cardiopulmonary bypass, acute cerebrovascular ischemia, peripheral vascular disease, diabetes mellitus, preeclampsia, and Alzheimer's disease. Clinical applications of whole blood flow cytometric assays of platelet function in these diseases may include identification of patients who would benefit from additional antiplatelet therapy and prediction of ischemic events. Circulating monocyte-platelet aggregates appear to be a more sensitive marker of in vivo platelet activation than circulating P-selectin-positive platelets. Flow cytometry can also be used in the following clinical settings: monitoring of glycoprotein IIb-IIIa antagonist therapy, diagnosis of inherited deficiencies of platelet surface glycoproteins, diagnosis of storage pool disease, diagnosis of heparin-induced thrombocytopenia, and measurement of the rate of thrombopoiesis.     

Oral conjugated equine estrogen increases plasma von Willebrand factor in postmenopausal women

OBJECTIVES: We sought to test whether one month of daily oral conjugated equine estrogen (CEE) or transdermal estradiol alters hemostatic factors in postmenopausal subjects. BACKGROUND: Estrogen replacement therapy and hormonal replacement therapy (HRT) effect an early increase in cardiovascular events in postmenopausal women. Circulating plasma von Willebrand factor (vWF) antigen is a marker of generalized endothelial dysfunction and atherothrombosis. METHODS: Thirty-eight healthy postmenopausal women (average 59 +/- 7 years) were randomized to receive daily oral CEE, 0.625 mg (n = 21); transdermal estradiol, 0.1 mg/day (n = 7); or oral placebo (n = 10) for one month. Blood samples were collected at baseline and after two weeks and four weeks of therapy for measurement of circulating plasma hormones, lipid concentrations, and hemostatic factors. RESULTS: Oral CEE decreased total cholesterol (p < 0.01) and low-density lipoprotein cholesterol (p < 0.01), although it increased both triglycerides (p < 0.05) and high-density lipoprotein cholesterol (p < 0.01). Transdermal estradiol had no significant effect on lipids. Plasminogen activator inhibitor-1 antigen declined in both oral CEE and transdermal estradiol users, but did not achieve statistical significance. Fibrin D-dimer antigen did not vary significantly in any group. However, oral CEE users had a significant increase in vWF from baseline to four weeks (p < 0.03) and a decrease in tissue-type plasminogen activator antigen from baseline to four weeks (p < 0.004), which was significantly different from the change observed in the transdermal estradiol group (p < 0.05). CONCLUSIONS: These data suggest that the oral CEE-mediated increase in plasma vWF may have clinical relevance given the early atherothrombotic effects of HRT in postmenopausal women.     

Human platelet-derived mitogens. I. Identification of insulinlike growth factors I and II by purification and N alpha amino acid sequence analysis

Human platelet lysates contained potent mitogenic activities for MCF-7 human breast-cancer cells in serum-free-defined media. Because these activities were not replaced by known platelet mitogens, such as platelet-derived growth factor or transforming growth factor beta, we sought to identify the breast cancer cell mitogens by purification and N alpha amino-acid sequencing. Acetic acid extracts of outdated human platelets were concentrated by ammonium sulfate precipitation and fractionated on Sephadex G-50 and Bio-Gel P-10 columns in 0.5 mol/L acetic acid. Two major activities were resolved by molecular sieve methods and fractionated further by reverse-phase high-performance liquid chromatography (HPLC). Purifications (70,000 to 870,000-fold) were accomplished yielding mol wt 7,400 products that were homogeneous as determined by iodination, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and autoradiography. The factors were identified as insulinlike growth factor I (IGF-I) and II (IGF-II) and truncated IGF-I by N alpha amino acid microsequencing. In dose-response experiments, platelet-derived IGF-I and IGF-II promoted multiple divisions of the MCF-7 cells with ED50 values of 12 and 100 pg/mL, respectively. The specific activities and other bioassay characteristics of platelet-derived IGF-I and IGF-II were similar to those of recombinant-produced human growth factors. This is the first report of the purification of insulinlike growth factors from human platelet lysates.     

Dietary l-Arginine Supplementation Normalizes Platelet Aggregation in Hypercholesterolemic Humans

Objectives. The present study was designed to test the hypothesis that long-term dietary supplementation with the nitric oxide precursor l-arginine would enhance vascular or platelet-derived nitric oxide activity, or both, and thereby inhibit platelet reactivity in hypercholesterolemic humans.Background. We have shown that reduced vascular activity of nitric oxide in hypercholesterolemic rabbits can be restored by l-arginine supplementation. The improvement in nitric oxide activity is associated with an inhibition of platelet aggregation ex vivo. This effect is most likely due to increased elaboration of endothelium- or platelet-derived nitric oxide, or both, because the inhibition of platelet reactivity was associated with elevation of intraplatelet cyclic guanosine monophosphate and was reversed by the nitric oxide synthase antagonist N-methyl-arginine.Methods. In a double-blinded, randomized, placebo-controlled trial, hypercholesterolemic patients were assigned to l-arginine hydrochloride, 8.4 g/day orally, or placebo for 2 weeks. Platelet-rich plasma was obtained for aggregometry induced by collagen (1 to 10 μg/ml) at four points: baseline, after 2 weeks of treatment, after a 2-week washout and after a long-term washout of 16 weeks on average. Aggregation was quantified by light transmittance and expressed as a percent transmittance observed with platelet-poor plasma.Results. Compared with normocholesterolemic control subjects, platelets from hypercholesterolemic subjects stimulated with 5 μg/ml of collagen showed increased aggregability (68.6% in hypercholesterolemic patients vs. 54.5% in normocholesterolemic control subjects, p ≤ 0.02). After 2 weeks of treatment with l-arginine (but not placebo), platelet reactivity was modestly reduced; this effect persisted for 2 weeks after discontinuation of arginine (52.6% in arginine-treated patients vs. 65.1% in normocholesterolemic control subjects, p = 0.07). After 18 weeks (i.e., 16 weeks after discontinuing arginine treatment), the platelets of hypercholesterolemic patients once again became hyperaggregable, and the extent of platelet aggregation was significantly increased compared with the 4-week point (73.6% after vs. 52.6% during arginine treatment, p < 0.01). No significant change in platelet reactivity was seen in placebo-treated hypercholesterolemic patients throughout the study. l-Arginine treatment was well tolerated without side effects.Conclusions. This double-blinded, placebo-controlled study demonstrates that dietary supplementation with l-arginine can modestly attenuate the increased platelet reactivity seen in hypercholesterolemic patients. The data are consistent with our previous studies in hypercholesterolemic animals, demonstrating that l-arginine restores endogenous nitric oxide activity and inhibits platelet aggregation. Enhancement of endogenous nitric oxide activity is a potential novel therapeutic strategy worthy of further study.(J Am Coll Cardiol 1997;29:479–85)     

Increased platelet-derived mitogenic activity in plasma of young patients with coronary atherosclerosis

The early state of atherosclerosis is characterized by a nodular proliferation of smooth muscle cells in the arterial intima. It has been suggested that this proliferation is initiated by platelet-derived growth factor (PDGF) released from aggregating platelets in connection with endothelial injury. In the present study platelet reactivity and mitogenic activity of plasma and serum were compared in young male survivors of myocardial infarction with angiographically demonstrable coronary atherosclerosis and in healthy subjects of similar age. Young post-infarction patients with coronary atherosclerosis had lower ED50 values of ADP-induced platelet aggregation. Furthermore plasma and serum from the patients contained increased amounts of mitogenic activity. Experiments using antibodies against platelet-derived growth factor indicated that the increase in mitogenic activity represented elevated concentrations of free PDGF growth factor in plasma. The results raise the possibility of a connection between increased levels of free PDGF and the proliferative reaction that characterizes early lesion progression.